Wireless network having joint power and data rate adaptation

ABSTRACT

A wireless network includes transmission power and data rate adaptation based upon quality experienced by the user.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending application Ser. No.11/899,722, entitled “Wireless Network Having Joint Power and Data RateAdaptation,” filed Sep. 6, 2007, which issued on Apr. 26, 2011 as U.S.Pat. No. 7,933,251, which is a continuation of application Ser. No.11/203,386, entitled “Wireless Network Having Joint Power and Data RateAdaptation,” filed Aug. 12, 2005, which issued on Oct. 9, 2007 as U.S.Pat. No. 7,280,514, which is a continuation of application Ser. No.10/001,650, entitled “Wireless Network Having Joint Power and Data RateAdaptation,” filed Oct. 31, 2001, which issued on Sep. 27, 2005 as U.S.Pat. No. 6,950,670.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable.

FIELD OF THE INVENTION

The present invention relates generally to communication systems and,more particularly, to wireless networks.

BACKGROUND OF THE INVENTION

As is known in the art, wireless communication systems, such as EnhancedData rate for GSM Evolution (EDGE), Wideband Code Division. MultipleAccess (WCDMA), and High Data Rate (HDR) CDMA, have radio resources thatcan be assigned to users adaptively based upon their channel conditionsin order to optimize the overall system performance. The overall systemperformance for wireless systems is typically measured by the spectrumefficiency, in kbps/MHz/site, subject to a given user performancerequirement (e.g. 90% of average user throughput should be higher than50 kbps).

In the EDGE system, a radio resource includes a transmission power and atransmission format (modulation/coding). Each transmission formatcorresponds to one transmission rate. The transmission format is changeddynamically according to the measured channel conditions for maximizinguser throughput. Power control can also be used to enhance systemperformance.

In WCDMA, the radio resources are represented by a transmission powerand a spreading code with different spreading factors (i.e. OrthogonalVariable Spreading Factor (OVSF)). Different transmission rates can beachieved by varying the transmission power and code allocation. HDR issimilar to WCDMA as both transmission power and spreading code can bevaried to maximize the system throughput. However, determining anoptimal power and transmission rate allocation for all the system usersis quite challenging. In addition, known systems require a centralcontroller for acquiring knowledge of propagation conditions for all ofthe active users in the system. Such systems are unable to achieve theoptimal allocation of scarce radio resources.

It would, therefore, be desirable to provide a wireless system thatovercomes the aforesaid and other disadvantages.

SUMMARY OF THE INVENTION

The present invention provides a wireless network having decentralizedtransmission power and data rate adaptation hued upon user link quality.With this arrangement, power and data rates move to optimal levels basedupon feedback from the mobile stations served by the network. While theinvention is primarily shown and described in conjunction with mobiledevices served by a wireless network, it is understood that theinvention is applicable to networks in general in which power and datarate adaptation is desirable.

In one aspect of the invention, a wireless network includes a pluralityof mobile stations served by respective base stations. Each mobilestation remains at a current transmission rate until the mobile stationmeets predetermined performance criteria to increase or decrease thetransmission rate for the next frame, for example. As the transmissionrate is adjusted, the transmission power is modified to achieve therequired level of performance for the transmission rate.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a schematic depiction of a wireless network havingtransmission power and data rate adaptation in accordance with thepresent invention;

FIG. 2 is a schematic depiction of an exemplary frame that can begenerated by the system of FIG. 1;

FIG. 3 is a flow diagram showing an exemplary sequence of steps forimplementing transmission power and data rate adaptation in a wirelessnetwork in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows an exemplary wireless network 100 having dynamic powercontrol and data rate adaptation in accordance with the presentinvention. The network 100 includes a plurality of base stations BS1-7each serving a respective sector or cell C1-7. Mobile stations MS1-N canbe located in the various cells C1-7 and transmit and receive data fromthe serving base station BS.

While the invention is primarily described in conjunction with aWideband Code Division Multiple Access (WCDMA) system, it is understoodthat the invention is applicable to other wireless systems, such as EDGEand HDR, having a variety of modulation formats including Time DivisionMultiplexing (TDM), Code Division Multiplexing (CDM), Frequency DivisionMultiplexing (FDM), and combinations of these formats.

The invention provides a decentralized, heuristic power/rate adaptationtechnique that enhances overall system performance. In general, anactive mobile station MS remains at a current transmission rate untilthe mobile station MS meets specified performance criteria. In anexemplary embodiment, a first criterion, such as a threshold linkquality measure, is used to qualify the mobile station to step up to thenext higher transmission rate. A second criterion is used to step downthe data rate to the next lower transmission rate. In other words, themobile station transmission rate follows a series of steps untilarriving at the optimal transmission rate for that mobile station. Inaddition, at each step, power control is used to achieve the requiredlevel of performance for the corresponding transmission rate.

Referring now to FIG. 2, an exemplary time structure is shown for whichjoint power and rate adaptation in accordance with the present inventionis implemented. Let k (not shown) denote the transmission rate index,which ranges from 1 to N and corresponds to an actual transmission rateof R(k) (e.g. R(k)=12×2^((k−1)) kbps). The joint power and rateadaptation algorithm works as follows for the exemplary WCDMA-type timestructure shown. Time is divided into time slots 200 a-M, which aregrouped into a frame 202. The channel condition, e.g.Signal-to-Interference-plus-Noise Ratio (SLNR), can be measured andpower control can be performed on a slot-by-slot basis.

In the exemplary embodiment shown, each slot 200 includes a downlinkphysical data channel (DPCCH) portion 204 containing a predeterminednumber of data bits and a downlink physical control channel (DPCCH)portion 206. The DPCCH portion 206 further includes a transmit powercontrol (TPC) portion 208 and a transmit format combination indicatorportion 210 that combine to adaptively adjust power and transmissionrate, as described more fully below.

In one particular embodiment, the transmitted data is decoded afterreceiving the entire flame 202. It is understood that the illustratedtime structure is intended to facilitate an understanding of theinvention and the inventive algorithm is independent of this exemplarystructure.

FIG. 3 shows an exemplary sequence of steps for implementing joint powerand rate adaptation in accordance with the present invention. In oneembodiment, an initial transmission rate R(0) is selected based uponSINR measurements so that R(0) does not exceed the maximum ratesupported by the code and power currently available at the serving basestation.

In step 300, the SINR is measured to determine link performance. In step302, the measured SINR is used to adjust transmission power towards thepower control target specified for the selected transmission rate (k).That is, it is determined whether the measured SINR level is greaterthan the target SINR level; i.e., whether SINR_(i)>SINR_(target)(k),where SINR_(i), is the measured SINR at the ith time slot andSINR_(target)(k) is the target SINR for the selected transmission ratek. If so, in step 304, the transmission power is decreased by apredetermined amount Δ dB, e.g. 1 dB. If not, in step 306, it isdetermined whether the measured level is less then the target level,i.e., whether SINR_(i)<SINR_(taret)(k). If it is, then in step 308 thetransmission power is increased by a predetermined amount Δ dB, e.g. 1dB. Otherwise, the current transmission power is maintained in step 310.It will be readily apparent to one of ordinary skill in the art that thetransmission power up and down step adjustments can vary to meet therequirements of a particular application. In addition, it is understoodthat the up and down steps need not be the same amount.

At the end of each frame, for example, as determined in step 311, themobile station determines the average received SINR in the previousframe (SINR_(avg)) in step 312. In step 314, it is determined whetherthe average SINR (SINR_(avg)) is greater than or equal to apredetermined threshold for the current or selected rate(SINR_(low)(k)), i.e., whether SINR_(avg)>=SINR_(low)(k). If so, then arate adaptation counter is incremented, i.e., C_(up)=C_(up)+1, in step316. Otherwise, in step 318 the rate adaptation counter is decremented,i.e., C_(up)=C_(up)−1. While counters are used to step the transmissionrate up and down in the illustrative embodiment, alternative mechanismswill be readily apparent to one of ordinary skill in the art.

In step 320, it is determined whether the rate adaptation counter hascrossed a predetermined up threshold, i.e., whether C_(up)>THR_(up). Ifit has, then in step 322 the transmission rate is updated. In anexemplary embodiment, the transmission rate for the next frame (R(n+1))is updated to reflect the minimum of the rate of the current frame plusone (R(n)+1) and a predetermined maximum supported rate (R_(max)), i.e.,R(n+1)=min(R(n)+1, R_(max)). If the rate adaptation counter was notgreater than the up threshold, as determined in step 320, then in step324 it is determined whether the counter value is less than apredetermined down threshold, i.e., whether C_(up)<THR_(down). In oneparticular embodiment, the up threshold THR_(up) is three, the downthreshold THR_(down) is minus three, and R_(max) is the maximumtransmission rate supported by the system.

If the rate adaptation counter was less than the predetermined downthreshold, then in step 326 the transmission rate for the next frame(R(n+1)) is updated to reflect the maximum of the rate for the currentframe minus one (R(n)−1) and one, i.e., R(n+1)=max(R(n)−1, 1). In oneparticular embodiment, a rate of one corresponds to a predeterminedminimum transmission rate. In step 328 it is determined whethertransmission to the mobile station should be delayed. If it isdetermined that the transmission should be delayed, then thetransmission rate is dropped to zero in step 330 by setting the rate tothe minimum of the current minus one and zero, i.e., (R(n+1)=min(R(n)−1,0)). If not, in step 332 the transmission rate remains unchanged, i.e.,R(n+1)=R(n). It is understood that the step of determining whether todrop the transmission rate to zero can be located in a variety oflocations in the flow sequence as well as interrupt driven.

The above steps are repeated to continually update the transmission rateand control the power to optimize the link quality based upon themeasured SINR. It is understood that a wide variety of link qualitymeasures can be utilized without departing from the present inventionprovided the measure enables relatively rapid power and rate adjustmentsas in the present invention.

The present invention provides a wireless system with joint power andtransmission rate adaptation. With this arrangement, the system isrelatively robust against estimation or selection errors. In addition,the system provides enhanced radio resource management. Further, thelimited radio spectrum can be utilized more efficiently so as to providehigher system capacity than known systems.

One skilled in the art will appreciate further features and advantagesof the invention based on the above-described embodiments. Accordingly,the invention is not to be limited by what has been particularly shownand described, except as indicated by the appended claims. Allpublications and references cited herein are expressly incorporatedherein by reference in their entirety.

What is claimed is:
 1. A method for jointly adapting power and datatransmission rate in a wideband code division multiple access wirelessnetwork, comprising: determining for a wireless base station of thenetwork a spreading code adjustment based on an average link quality ofat least one previous uplink frame; determining for the wireless basestation a transmit power adjustment based on a link quality of at leastone time slot of a current uplink frame; transmitting from the wirelessbase station a downlink frame having a time slot, the time slot of thedownlink frame comprising a downlink physical data channel portioncarrying payload data and a downlink physical control channel portion,the downlink physical control channel portion including: a transmitpower control portion containing information based on the transmit poweradjustment; and a transmit format combination indicator portioncontaining information based on the spreading code adjustment; andwherein determining the transmit power adjustment based on the linkquality of at least one time slot of a current uplink frame furthercomprises: stepping a rate adaption counter value based on a comparisonof the average link quality with a predetermined link quality threshold;and comparing the rate adaption counter value with upper and lower rateadaption counter thresholds.
 2. The method according to claim 1, whereindetermining a spreading code adjustment based on an average link qualityof at least one previous uplink frame further comprises: if the countervalue is greater than the upper rate adaptation counter threshold, thendetermining spreading code adjustment that results in a transmissionrate that is a minimum of a rate following a rate of the current uplinkframe in a transmission rate index, and a maximum supported transmissionrate.
 3. The method according to claim 1 wherein the wireless basestation has a wideband code division multiple access transmissioncapability and wherein transmitting a downlink frame comprisestransmitting the downlink frame using wideband code division multipleaccess protocols.
 4. The method according to claim 1, wherein the upperand lower rate adaptation counter thresholds are, respectively, positiveand negative integers.
 5. The method according to claim 1, whereindetermining a spreading code adjustment based on an average link qualityof at least one previous uplink frame further comprises: if the countervalue is less than the lower rate adaptation counter threshold, thendetermining a spreading code adjustment that results in a transmissionrate that is a minimum of a rate preceding a rate of the current uplinkframe in a transmission rate index, and a first rate in the transmissionrate index.
 6. The method according to claim 1, wherein the downlinkphysical data channel portion precedes the downlink physical controlchannel portion in the time slot of the downlink frame.
 7. The methodaccording to claim 1, further comprising: determining whether atransmission should be delayed; and if the transmission should bedelayed, determining a spreading code adjustment that results in atransmission rate of zero.
 8. The method according to claim 1, whereindetermining a transmit power adjustment based on a link quality of atleast one time slot of the current uplink frame further comprises:assigning a predetermined down amount to the transmit power adjustmentif the link quality is greater than a power control target range, andassigning a predetermined up amount to the transmit power adjustment ifthe link quality is lower than the power control target range.
 9. Themethod according to claim 1, wherein the link quality and the averagelink quality correspond to measuredsignal-to-interference-plus-noise-ratio levels.
 10. A tangiblecomputer-readable medium having computer readable instructions storedthereon for execution by a processor to perform a method for jointlyadapting power and data transmission rate in a wireless network,comprising: determining a spreading code adjustment based on an averagelink quality of at least one previous uplink frame; determining atransmit power adjustment based on a link quality of at least one timeslot of a current uplink frame; transmitting a downlink frame having atime slot, the time slot of the downlink frame comprising a downlinkphysical data channel portion carrying payload data and a downlinkphysical control channel portion, the downlink physical control channelportion including: a transmit power control portion containinginformation based on the transmit power adjustment; and a transmitformat combination indicator portion containing information based on thespreading code adjustment; and wherein determining the transmit poweradjustment based on the link quality of at least one time slot of acurrent uplink frame further comprises: stepping a rate adaption countervalue based on a comparison of the average link quality with apredetermined link quality threshold; and comparing the rate adaptioncounter value with upper and lower rate adaption counter thresholds. 11.The tangible computer-readable medium according to claim 10, whereindetermining a spreading code adjustment based on an average link qualityof at least one previous uplink frame further comprises: when thecounter value is greater than the upper rate adaptation counterthreshold, then determining spreading code adjustment that results in atransmission rate that is a minimum of a rate following a rate of thecurrent uplink frame in a transmission rate index, and a maximumsupported transmission rate.
 12. The tangible computer-readable mediumaccording to claim 10, wherein transmitting a downlink frame comprisestransmitting the downlink frame using wideband code division multipleaccess protocols.
 13. The tangible computer-readable medium according toclaim 10, wherein the upper and lower rate adaptation counter thresholdsare, respectively, positive and negative integers.
 14. The tangiblecomputer-readable medium according to claim 10, wherein determining aspreading code adjustment based on an average link quality of at leastone previous uplink frame further comprises: when the counter value isless than the lower rate adaptation counter threshold, then determininga spreading code adjustment that results in a transmission rate that isa minimum of a rate preceding a rate of the current uplink frame in atransmission rate index, and a first rate in the transmission rateindex.
 15. The tangible computer-readable medium according to claim 10,wherein the downlink physical data channel portion precedes the downlinkphysical control channel portion in the time slot of the downlink frame.16. The tangible computer-readable medium according to claim 10, whereinthe method further comprises: determining whether a transmission shouldbe delayed; and if the transmission should be delayed, determining aspreading code adjustment that results in a transmission rate of zero.17. The tangible computer-readable medium according to claim 10, whereindetermining a transmit power adjustment based on a link quality of atleast one time slot of the current uplink frame further comprises:assigning a predetermined down amount to the transmit power adjustmentif the link quality is greater than a power control target range, andassigning a predetermined up amount to the transmit power adjustment ifthe link quality is lower than the power control target range.
 18. Thetangible computer-readable medium according to claim 10, wherein thelink quality and the average link quality correspond to measuredsignal-to-interference-plus-noise-ratio levels.
 19. A method for jointlyadapting power and data transmission rate in a wideband code divisionmultiple access wireless network, comprising: determining for a wirelessbase station of the network a spreading code adjustment based on anaverage link quality of at least one previous uplink frame; determiningfor the wireless base station a transmit power adjustment based on alink quality of at least one time slot of a current uplink frame;transmitting from the wireless base station a downlink frame having atime slot, the time slot of the downlink frame comprising a downlinkphysical data channel portion carrying payload data and a downlinkphysical control channel portion, the downlink physical control channelportion including: a transmit power control portion containinginformation based on the transmit power adjustment; and a transmitformat combination indicator portion containing information based on thespreading code adjustment; determining whether a transmission should bedelayed; and if the transmission should be delayed, determining aspreading code adjustment that results in a transmission rate of zero.